1. Field of the Invention
This invention concerns a novel process for producing asphalt-blended polyurethane foams suitably used for sealing materials, sound-proofing or vibration-damping materials, etc.
2. Description of the Prior Art
Asphalt-blended polyurethane foams have hitherto been used as sealing materials for use in vehicles and in civil engineering, as well as sound-proofing or vibration-damping materials for use in vehicles and in general industries.
As the process for producing asphalt-blended polyurethane foams, there have been known the following processes:
(1) A process of melting and impregnating asphalts into flexible polyurethane foams having interconnected open cells, a process of impregnating an aqueous asphalt emulsion into flexible polyurethane foams followed by drying and, further, a process of impregnating an asphalt solution dissolved in a solvent into flexible polyurethane foams followed by drying (hereinafter referred to as "impregnation process"), PA0 (2) a process of preparing a urethane prepolymer by reacting a hydrophilic polyester polyol having an ethylene oxide content of greater than 15% with an organic isocyanate and then reacting to foam the prepolymer with an aqueous asphalt emulsion (hereinafter referred to as "foaming process A"), and PA0 (3) a process of blending asphalts previously with polyols compatible with asphalts such as polybutadiene polyol or the like and then mixing an organic isocyanate and like other ingredients followed by foaming (hereinafter referred to as "foaming process B").
Asphalt-blended polyurethane foams having water-proofness and sound-proofing or vibration-damping properties derived from asphalts can be obtained to any of these production processes.
However, since the asphalts are impregnated in previously formed flexible polyurethane foams in the impregnation process (1), it requires two steps for the production process and higher production cost as compared with the foaming process, as well as the impregnated asphalts may leach under high temperature causing sticking or contamination.
In the foaming process A above, an aqueous asphalt emulsion has to be prepared separately upon production of the polyurethane foams to require troublesome procedures for the production of foams. In addition, since the aqueous asphalt emulsion is used, it is difficult to optionally control the density of polyurethane foams by using an identical prepolymer, which results in disadvantages in that the natures of the resultant foams can not be varied with ease. Further, in view of the compatibility between the aqueous asphalt emulsion and the polyether polyol upon foaming the polyether polyol, a highly hydrophilic polyether polyol having 15% or more of ethylene oxide content has to be used to impose a restriction on the type of usable polyols, as well as the resultant foams swell upon contact with water to worsen the dimensional stability.
Further, the foaming process B is not practical since the resultant foams are expensive because of the use of a special polyol and because it can not attain the purpose of reducing the cost which is the merit of compositing the asphalts.
Moreover, although there have been proposed various attempts for producing asphalt-blended polyurethane foams comprising conventional polyurethane foams and asphalts composited thereto by means of the foaming process, since the polyoxyalkylene polyol and the asphalt as the main starting material for the conventional polyurethane foams are not compatible with but separated from each other, there have been few successful examples.
In view of the above, the present inventors have noticed that asphalts are compatible with organic isocyanates and already proposed a production process by forming a prepolymer through the reaction of a polyoxyalkylene polyol and an organic isocyanate, dissolving and blending asphalts with the prepolymer and then mixing to react water and a crosslinker with the blend to effect foaming (refer to the Japanese Patent Laid-Open No. 91213/1986).
However, since the viscosity of the blend comprising the prepolymer and the asphalt increases along with the increase in the blending amount of the asphalt in this process, there is a limit to the amount of the asphalt that can be dissolved and, further, the blend comprising the prepolymer and the asphalt increases the viscosity with an elapse of time to render the foaming instable.
In view of the above, there has been a demand for the development of a novel production process capable of blending the asphalt in a great amount and stably capable of producing asphalt-blended polyurethane foams suitably used as the sealing materials or sound-proofing or vibration-damping materials easily at a high production efficiency.